Propelling a bicycle requires a cyclist to exert a force sufficient to counteract several different types of forces which oppose the movement of the bicycle. A major force acting against movement is the drag induced by the bicycle's movement through the air. As a rider attempts to move faster, the drag forces become greater. Greater drag requires the rider to expend greater energy to overcome the drag. Thus, these forces become an important consideration in sports such as bicycle racing and triathlons.
A major source of drag in bicycle racing results from the flow of air over and around the bicycle wheels. Cyclists have attempted to reduce drag in wheels through the use of a "solid" or "disc" wheel. Such a wheel has no spokes, and thus eliminates the drag caused by the movement of air over the spokes and over and around the wheel rim.
Despite the apparent drag reducing advantage of solid wheels, many riders feel that the disadvantages inherent in such a structure render a solid wheel unsatisfactory for racing. The major source of this dissatisfaction stems from crosswind loading of the solid wheel. As wind forces perpendicular to the disc surface increase, an increased windloading force is transmitted from the disc surface to the bicycle handlebars. This requires the rider to apply a control force to the handlebars that varies as the windloading changes. Additionally, the force exerted by a sudden crosswind can destabilize the bicycle and rider and forward speed can be reduced.
Until recently, cyclists have been forced to choose either traditional spoked wheels with their inherent drag component or solid wheels with their inherent crosswind disadvantages. Recent attempts to reconcile these two types of wheels have led to a compromise wheel design. This design employs a limited number of solid spokes in conjunction with the bicycle rim. These wheels resemble a solid wheel with large "cutouts" in the disc to minimize the crosswind effects. Despite these efforts, the compromise designs can still suffer from objectionable crosswind windloading and drag and otherwise not have optimum aerodynamic or structural characteristics.
A need exists for a non-solid wheel with the low drag characteristics of a solid wheel. A need also exists for a wheel that is aerodynamic and has good crosswind stability.